3 / 7 Back-of-the-Envelope Estimation

Ten Gigabits Of Nothing

A design doc contains this paragraph:

At peak we ingest 1.2 GB per second across the fleet. Each ingest host has a 10 Gbps NIC, so one host can absorb 10 GB/s. That gives us roughly 8x headroom on a single host, and we will still run three for redundancy.

The first load test saturates the NIC on one host at peak. What is the actual headroom?

A

Unknowable from the doc, because NIC line rate is never reachable with real packet sizes.

B

About 8x. The arithmetic is right and the load test failed for some other reason, most likely interrupt handling.

C

About 1.04x, which is effectively none.

D

About 10.4x, because a 10 Gbps NIC carries 12.5 GB/s.